As part of our larger effort to understand unique aspects of HIV biochemistry that might be exploited in novel therapeutic approaches, we here focus on the critical dual roles of a single viral nucleocapsid component for both viral DNA integration and subsequent virion assembly. We can now show that distinct targeting signals essential for both functions are located in the same viral protein - matrix antigen pl7 (MA pl7). It has been known that myristoylation of MA pl7 provides the membrane targeting signal required for virion assembly at the cell surface, but our new preliminary information reveals that a specific peptide sequence near the amino terminus of MA pl7 acts as the nuclear localization signal (NLS) required for importation of the viral preintegration complex to the cell nucleus. Of particular importance, our pilot work shows that the NLS of MA pl7 is essential for HIV-1 replication in non-dividing cells, an attribute unique to the lentiviruses and of significant clinical importance in HIV infection. Although it is clear that host cell elements must interact with these opposing viral targeting signals, little or no information is available concerning the molecular mechanisms that underlie trafficking of viral components in HIV-infected cells. In this application we propose a detailed study of the critical role of MA pl7 and its gag precursor in the life cycle of HIV-1, with special emphasis on the interaction of countervailing signals during the transport of MA pl7 and p55 precursor to different subcellular compartments. To establish the role of MA pl7 in the formation and nuclear localization of HIV-1 preintegration complexes, we propose to characterize differential biochemical modifications of nuclear versus cytoplasmic forms of the viral proteins at the early (preintegration) steps immediately after infection, and to study the interactions of HIV-1 core proteins with viral genomic RNA and DNA. A second area of research will emphasize the identification and characterization of cellular factors interacting with HIV-1 MA pl7 and their role in the nuclear localization of the HIV-1 genome. These portions of the project should provide important new insights into the mechanisms which allow HIV to infect non-dividing cells. The nuclear localization signal is also likely to serve a role during viral assembly, and we propose to characterize nucleophilic and membranotropic forms of the gag polyprotein, and to analyze processing of the gag precursor as it relates to virion formation. It is expected that these studies will provide fundamental new insights into the process of HIV-1 infection and define novel targets for therapy aimed at interfering with nuclear targeting and virion assembly.